Recommendation for an SWR meter - RC Groups
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Dec 01, 2009, 10:05 PM
Engineer for Christ
IBCrazy's Avatar
Discussion

Recommendation for an SWR meter


Can anyone recommend a good SWR meter for my 900 MHz system that won't break the bank? The only ones I can find cost about $250. One with a power meter would be a plus.

Thanks,

-Alex
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Dec 01, 2009, 10:36 PM
Senior Gravity Checker
Tap into the RSSI pin on your video receiver with a voltmeter. Higher the voltage the better the received signal. About $10 for a meter. Cheap enough?

-Ken
Dec 01, 2009, 11:35 PM
I think my wheels fell off.
Thumb_number's Avatar
Hi Alex,

Been looking at this problem for a while. The best device I've used for tuning a home made 900Mhz dipole was a satellite meter. (I just happened to have one laying around). This just gives a dB figure of signal for a given freq. I used this to trim the dipole until I got the best dB numbers (about 87dB at 20m with an RV500mw). This method gives no real indication of good SWR, it just indicates the strongest raw signal. If one is good, the other must be OK right?? I dont know.

You should be able to find a cheap second hand satellite meter for reasonable $$$'s, it doesn't have to have a pretty spectrum display, just a level indication.

I've looked for SWR meters covering 900, and there's not much about. I've started looking at mobile phone companies to see what they use to tune antennas. I will post if anything comes up.

Have you a link to the one you found for $250?

Good luck.
Dec 02, 2009, 11:51 AM
Tom Para
Tom in Cincy's Avatar
If you want to do it right and on the cheap you need a directional coupler, a microwave detector (diode) , a load resistor and a voltmeter.
Look on Ebay for the above items. you will need to decide which connector system you will use. All up costs should be between $50-$80. I built a swr meter out of these components and it is accurate thru the 5.8 Ghz band.
I have found the pre built antennas to be very well matched. However the high gain patch antennas are pretty narrow and your channel selection will make a big difference in the SWR. BTW you can measure the voltage across the resistor and get an idea what the power outputs are.
Here is a link for a typical directional coupler http://cgi.ebay.com/narda-Model-3041...item45ef8263d2

tp
Last edited by Tom in Cincy; Dec 03, 2009 at 01:10 AM. Reason: no need for a special resistor/power is calculated across the resistor
Dec 02, 2009, 01:03 PM
JettPilot's Avatar
Quote:
Originally Posted by Tom in Cincy

Here is a link for a typical directional coupler http://cgi.ebay.com/narda-Model-3041...item45ef8263d2

tp
That is a great find, that coupler probably cost over 500 dollars new An swr meter that would read though 2.4 GHZ would be great

Mike
Dec 02, 2009, 03:38 PM
Born to Live - Live to Fly !
stevekott's Avatar
I know you can tune a piano but you can't tuna fish.

How can you tune a 900Mhz antenna even if you could read the SWR or RSSI ?
Dec 02, 2009, 03:58 PM
Registered User
http://www.rfparts.com/diamond/sx1100.html

900 - 2.5
http://www.wlanparts.com/product/CN-...00mW2W20W.html

Eham review for 900-2.5 SWR Meter
http://www.eham.net/reviews/detail/650
Last edited by EdHall; Dec 02, 2009 at 04:05 PM.
Dec 02, 2009, 04:27 PM
JettPilot's Avatar
Quote:
Originally Posted by stevekott
I know you can tune a piano but you can't tuna fish.

How can you tune a 900Mhz antenna even if you could read the SWR or RSSI ?
I make my own 900 MHZ antennas, I would adjust the leingth of the antenna to tune it. Right now, I just use calculated leingth, I have no idea how well its SWR is matched.

Mike
Dec 02, 2009, 04:58 PM
Registered User
if the transmitter remails fairly cool the swr is probbaly good enough if it gets hot it isn't
Dec 02, 2009, 05:21 PM
Live FPV or Die
VRflyer's Avatar
Quote:
Originally Posted by cmulder
if the transmitter remails fairly cool the swr is probbaly good enough if it gets hot it isn't
so with a temperature probe glue on the tx and patience I would trim the antenna lenght to get the coolest temperature. I will get a try.
Dec 02, 2009, 05:48 PM
Engineer for Christ
IBCrazy's Avatar
The temp probe isn't necessarily a good idea. Granted temperature and SWR are related, but loosely. I would be willing to bet the TX stays cooler with no antenna at all than with a well tuned antenna.

I might try Tom in Cincy's idea. Granted, not truly SWR, but max power out will be found at best SWR.
Dec 03, 2009, 12:57 AM
Tom Para
Tom in Cincy's Avatar
Quote:
Originally Posted by IBCrazy
I might try Tom in Cincy's idea. Granted, not truly SWR, but max power out will be found at best SWR.
Actually it is truly SWR. A measurement is made with the directional coupler hooked up. Then the input connection/output connection on the "DC" is reversed and another reading is taken. A ratio is then calculated between the 2 readings. Thats why its called a directional coupler.

The high gain patch antennas would be nearly impossible to tune. i used my set-up to verify the accuracy of a 4 bay 2.4Ghz patch. These are the ones claiming 14dbi. I can say they did a very good job building that antenna. They had it tuned perfectly in the center of the band. As the gain of an antenna goes up the bandwidth and beamwidth become much more narrow. My SWR meter showed the best signal would be achieved by using a center frequency on 2.4
Dec 03, 2009, 01:50 PM
Born to Live - Live to Fly !
stevekott's Avatar
I have one of these ubiquiti frequency analyzers for 900Mhz and another for 2.4Ghz. They are relatively cheap at $59 and with a pc they give a lot of information.

I use it to check frequency use at a site and it helps determine if I use 900Mhz or 2.4Ghz based on the frequency use footprint.

It does give a peak power at a given freq in db. You might be able to use that in tuning an antenna to peak power.

It was also helpful to me at finding out the problem with an 'off frequency' transmitter that was always giving me bad performance. I had no clue how to fix it but I quit using it.

http://www.streakwave.com/Itemdesc.a...w9-EXT&eq=&Tp=
Last edited by stevekott; Jan 10, 2010 at 01:07 PM.


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